This invention relates generally to cartridge-type electrical fuses, and more particularly to a mating device which facilitates insertion of such fuses into a fuse holder and the removal thereof, the fuse-mate also carrying out other useful functions.
A fuse is a protective device containing a short length of special wire that melts when the current therethrough exceeds the rated value for a given period. Because the fuse is inserted in series with the circuit to be protected, it opens this circuit automatically in the event of an unacceptable overload.
The fuse commonly used in conjunction with electronic equipment is of the so-called cartridge type. This is constituted by a tubular casing of glass or other clear insulating material whose ends are enclosed by metal terminal caps, the fuse wire extending through the casing and bridging the caps. Since the fuse wire is visible through the transparent casing, should an overload occur which melts the wire, the blown condition of the fuse then becomes evident. In some cases, the casing is of opaque or ceramic material.
Cartridge fuses are socketed in holders formed by an insulating base on which a pair of metal spring clips is mounted to engage the terminal caps of the fuse, the circuit connections being made to the clips. In many instances, an array of parallel holders are formed on a common base so that the fuses are then very close to each other. Normally, to install a fuse, one grips the casing thereof between the thumb and forefinger and then pushes the fuse into the holder clips. And to remove a fuse from the holder, one again grips the casing with the fingers to pull the fuse from the holder clips.
To insure efficient electrical contact between the holder clips and the fuse terminal caps, the clips are designed to apply a substantial clamping pressure on the caps. These pressures make insertion and removal of the fuse quite difficult, which difficulty is compounded when the fuses are small or where a family of fuses are very close to each other. Moreover, because at least one holder clip is alive, and the gripping fingers are quite close to the terminal caps, there is a danger of shock, particularly if resistance is experienced in removing or inserting a fuse in the course of which the fingers are shifted toward the caps.
Because of problems encountered in removing cartridge type fuses, the use of screw drivers to pry the fuse from the holder is not uncommon. This can lead not only to fracture of the relatively delicate fuse casing, but it may also result in the short-circuiting of adjacent fuse holders.
In our copending application, above-identified, there is disclosed a fuse-mate adapted to facilitate the insertion and removal of a cartridge-type fuse. This fuse-mate, which is highly compact, may be permanently clipped onto a fuse whereby even when an array of fuses is arrayed in holders placed in close proximity to each other, there is no interference between adjacent mated fuses, and any mated fuse may be inserted or withdrawn from the array without difficulty.
A fuse-mate of the type disclosed in our copending application is molded of synthetic plastic material having good insulating properties and adequate structural strength, the fuse mate being configured to define a pair of elongated resilient clip-on jaws whose length is slightly shorter than the length of the tubular casing of the fuse to be engaged thereby between the end caps, the jaws being adapted to spread apart and embrace the casing.
The jaws project below and are integral with the underside of a rectangular shield which protectively covers the entire fuse and the "live" electrical holder clips thereunder to obviate the danger of shock. Formed on the upper side of the shield and integral therewith is a handle having concave sides to define finger depressions and a face which lends itself to marking.
In a fuse-mate of the type disclosed in our copending application, the jaws must have sufficient flexibility to make it possible to snap the fuse between the jaws. When one seeks to manually extract from its holder a cartridge fuse coupled to the fuse-mate, the outward force then applied to the handle of the fuse-mate will act to dilate the flexible jaws if the holder refuses to release the fuse. This situation arises should the spring clips of the holder be so tight as to resist flexing when one applies an outward pulling force to the fuse-mate. Thus instead of extracting the fuse, the jaws of the fuse-mate are then disengaged from the fuse which stays behind in the holder.
To overcome this problem, the fuse-mate may be designed with stiffened jaws so that the jaws firmly grip the tubular casing and are not disengaged therefrom when an outward pulling force is applied. But a structure of this type has a disadvantage, for it then becomes difficult to snap the fuse into the jaws of the fuse-mate.